Ignition system

ABSTRACT

An ignition system is described wherein a magnetic pulse is producted in a distributor, the pulse is amplified and used to bias into saturation a switching transistor in the circuit to the primary of an ignition coil. The ignition circuit is open for the major period of operation and is only closed for a sufficient time to reach saturation or near-saturation current in the primary of the coil. It has been found that the magnetic pick-up unit provides an increasing angle of dwell with increasing engine speed, thereby permitting use of a narrow band of dwell degrees. This permits the design of a single circuit which is compatible with all existing ignition coils and ballast resistors. The system is, therefore, ideally suited for the retrofit market since it minimizes the number of parts which must be replaced to only a cam flux wheel, a magnetic pick-up coil and the amplifier and switching network. The circuit also includes pulse-generating means which is operative at low engine speeds such as during starting to supplement the pulse from the pick-up coil and trigger the switching transistor.

United States Patent Long 1 51 Sept. 30, 1975 IGNITION SYSTEM [57] ABSTRACT [75] Inventor: Le lie T. L O C mi An ignition system is described wherein a magnetic I 1 pulse is producted in a distributor, the pulse is ampli [73] Asslgnec' l Enterpnses Midway Clty tied and used to bias into saturation a switching tran Cdhf sister in the circuit to the primary of an ignition coil. [22] Filed: July 26, 1973 The ignition circuit is open for the major period of operation and is only closed for a sufficient time to reach [21 1 Appl' 382324 saturation or near-saturation current in the primary of the coil. It has been found that the magnetic pick-up [52] US. Cl 123/148 E; 315/209 T unit provides an increasing angle of dwell with in- [51] Int. Cl. F02p 3/02 creasing engine speed, thereby permitting use of a nar- [58] Field of Search 123/148 E; 315/209 T row band of dwell degrees. This permits the design of a single circuit which is compatible with all existing [56] References Cited ignition coils and ballast resistors. The system is UNITED STATES PATENTS therefore. ideally suited for the retrofit market since it 3.072 s24 H1963 Short .v 123/148 E mlmmlzcs the number of parts whlcll mllst be replaced $250,954 5/1966 Konopu h 123/148 E to only a cam flux wheel a magnetic pick-up coil and 3251164 5/1966 Konopu h 123/148 E the amplifier and switching network. The circuit also 3353185 5/1966 Morrison 133/148 E includes pulse-generating means which is operative at 3.291109 12/1966 Ncapolitukisv 123/148 E low engine speeds such as during starting to supple- 3,357.416 12/1967 Huntzinger... 123/148 E ment the pulse from the pick-up coil and trigger the 3 390 668 7/1968 Hufton i E transistor 1791.364 2/1974 Saita 123/148 E Primary E.\amitterManucl A. Antonak'tls Assistant E.\'ttminerJoseph Cangelosi Attorney, Agent, or FirmRobert E. Strauss 14 Claims, 4 Drawing Figures US. Patent Sept. 30,1975

FIGURE 1 m M -l DEGREES ROTATION FIGURE 4- menus ROTATION FCJURE 2.

. 1 IGNITION SYSTEM BACKGROUND OF THE INVENTION The Kettering ignition system has been used without any substantial modification for many years. This system employs a pair of breaker points, which are activated between open and closed positions by a cam on the shaft of the distributor of an engine. The action of these points open and close an electrical circuit through the primanry windings of a transformer. The collapse of the magnetic field when the circuit is opened induces a high voltage in the transformer sec ondary which is directed to the appropriate spark plug by a rotor.

This ignition system requires a fair amount of maintenance since the mechanically driven breaker points wear and pit, resulting in improper and poor ignition. The concern over pollutants in exhaust emissions has imparted a criticality to the maintenance of proper engine ignition and the tolerance to wear of these systems is lessening.

Because the points are opened and closed by a cam, the degrees of rotation of the engine during the closed period (dwell) does not change with engine speed. The time the points remain closed does vary inversely with engine speed and a broad band of dwell degrees is necessary to insure that adequate dwell time is present at the higher engine speeds to achieve current saturation in the primary windings of the ignition coil. The conventional system is, therefore, affected substantially by engine speed and, at best, represents a compromise of high and low speed engine performance.

A number of point-less ignition systems have been proposed and are currently available on new cars. These systems are expensive and generally can not be adapted to retrofit older cars without major and costly alterations, such as replacement of the distributor, ballast resistor and/or ignition coil. Accordingly, there is a need for a simple, maintenance-free, solid state igni tion system which can be integrated into the conventional engine ignition systems with a minimum of replacement parts. Ideally, such an ignition system should be directly interchangeable with the contact point assembly of a conventional ignition system and should use the existing ballast resistor and ignition coil to obtain the necessary high voltage spark discharge. Preferably, the system should perform relatively independently of engine speed to permit a consistent and narrow band of dwell degrees.

BRIEF DESCRIPTION OF THE INVENTION This invention comprises a pulse amplification means that is entirely solid-state and that can be used to control the supply of electrical current to the primary of the coil of a conventional ignition system to obtain the necessary induced high voltage in the coil secondary windings.

This means comprises a pointless, voltage-pulse generator which includes a flux wheel, preferably one that fits over the cam of an existing distributor, and a pickup coil assembly that preferably is interchangeable with the conventional contact point assembly. The pick-up coil includes a permanent magnet and pole piece which is surrounded by the coil. This pick-up coil is connected to the base-emitter circuit of a transistor ampli fier the output of which is used to bias a switching transistor into saturation through an impedance matching means which is preferably a transistor in an emitterfollower network. The switching transistor is connected in the circuit to the primary of the conventional ignition coil. A supplemental voltage pulse amplifier means in the form of a capacitor is also connected in the baseemitter circuit of the amplifier, parallel to the pick-up coil, to provide a voltage pulse that supplements the pulse from the pick-up coil and insures firing of the ignition at low speeds.

BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in the accompanying drawings, of which:

FIG. 1 illustrates the ignition system components and circuits;

FIG. 2 illustrates a typical wave form in the circuit;

FIG. 3 illustrates an alternative pick-up coil assem bly; and

FIG. 4 illustrates the voltage wave form in the primary of the ignition coil.

DESCRIPTION OF THE PREFERRED AND ILLUSTRATED EMBODIMENTS The circuit is illustrated in FIG. 1 as adapted for negative ground electrical systems. The positive terminal of the battery is connected by connector 10 through ignition switch 12 to capacitor 14. Collector 22 of a PNP transistor is connected to the negative ground through current-limiting resistor 24. The base-emitter circuit of transistor 20 includes resistor 18 and coil 26 which is the pickup coil of the distributor. One side of capacitor 14 is connected in this circuit between resistor 18 and coil 26 and parallel to coil 26.

The distributor cam 30 which is commonly used to actuate the breaker points is fitted with a magnetic flux wheel 32 that is formed of material having a high magnetic permeability and low magnetic retentiveness, i.e., the so-called soft magnetic materials. Examples of these are iron and alloys thereof with major amounts of nickel and, optionally, lesser amounts of molybdenum, silicon, chromium and aluminum such as Permalloy, MoPermalloy, Supermalloy, Monimax, Sinimax, Numetal, Deltamax, Isoperm, Copernik, Perminvai, etc. The flux wheel can be cast, forged, machined or molded of powered metals. The wheel 32 has a plurality of upstanding ribs 34 evenly spaced about its periph' ery, one for each cylinder and is indexed with its ribs oriented on the cam to induce a maximum voltage change in pick-up coil 26 at approximately the same time as when conventional contact points are opened by the cam. The exact orientation for any particular engine make and design can readily be determined by the desired firing position. Generally, the ribs of the flux wheel are at a slightly advanced position in the direction of rotation by at least several degrees from the location on the cam where the conventional points are opened.

The conventional breaker point assembly that is carried by the breaker plate 42 of the distributor has been replaced with the pick-up coil assembly 28 which includes a permanent magnet 36 with a pole piece 38 which is mounted in radial opposition to ribs 34 of wheel 32. This assembly with wheel 32 forms a magnetic flux path shown in broken lines from one pole of the magnet through pole piece 38, rib 34, cam 30, distributor shaft 40, the distributor bearings, not shown, and breaker plate 42 to the opposite pole of magnet 36.

The air gap and magnetic reluctance of this magnetic flux path is greatly affected by rotation of ribs 34 into and out of alignment with pole piece 38. This cyclic variation of the flux path, which is in response to one half the speed of rotation of the engine crankshaft in a four-cycle engine, induces a cyclic voltage in pick-up coil 26 which is shown in FIG. 2.

FIG. 3 shows an alternative design of a pick-up coil and magnet assembly. In this design, the coil 26 surrounds the bight of a generally U-shaped bracket 25. Permanent magnet 36 is mounted on the short leg 27 of bracket 25 and is sandwiched between this leg and upper plate 37. The long leg 39 of bracket 25 and plate 37 form a pair of pole pieces which are in vertical alignment. Preferably, the outboard ends of these pole pieces are chamfered to form tips of the same width as the edges of ribs 34 of wheel 32. The magnetic flux path of this assembly is shown in broken lines through plate 37, a rib 34 of flux wheel 32, leg 39 and return to the magnet through the bight of bracket 25. This design avoids the dependency of the flux path on the various parts of the distributor.

The collector of transistor is connected, as shown in FIG. 1, to the base 47 of NPN transistor 48 in an emitter-follower network through resistor 46. The emitter-base circuit for this transistor is formed by resistor 50, the common ground and resistors 24 and 46. Collector 52 of transistor 48 is connected to positive lead 60 from the battery through resistor 54.

The positive lead 60 is attached through the conventional ignition ballast resistor 61 to the primary winding 62 of the conventional ignition coil 64. The other terminal of winding 62 is connected by conductor 66 to the collector 68 of the NPN transistor 70. The emitterbase circuit for this transistor is formed by resistor 50 and conductor 74 which extends to the base and grounded conductor 72 that extends to the emitter of transistor 70. A Zener diode 71 is connected between ground conductor 72 and conductor 66 in parallel to transistor 70.

One terminal of the secondary winding of the ignition coil is connected to the negative or ground post 63 of the coil by an internal conductor 65 and at its opposite end to the high tension center post 78. Conductor 79 is the high voltage lead to the center post of the distributor.

As shown in FIG. 2, the induced voltage in coil 26 appears in a cyclic variation about the applied battery voltage, line BV, as a functiion of degrees of rotation of the distributor shaft. Induced voltage reaches a maximum negative amplitude when a rib 34 moves opposite pole piece 38 and then rapidly reverses to a positive maximum as the rib 34 rotates past and separates from the pole piece. The induced voltage builds up more slowly in this coil then the extremely rapid change which occurs when the rib 34 rotates past pole piece 38 and a sudden reversal of voltage occurs. The induced voltage in pick-up coil 26 is shown by the broken line and corresponds to the open circuit voltage for this coil.

During normal operation of the engine, above about 100 revolutions per minute, the induced voltage in coil 26 supplies a voltage pulse of sufficient magnitude in the emitter-base circuit to bias transistor 20 into an amplification mode; this corresponds to the value of V shown in FIG. 2. When this occurs, transistor 20 functions as an amplifier, permitting current flow from the positive battery terminal, switch 12 and current limiting resistor 24 to the negative ground.

At speeds below about 100 revolutions per minute, typical of engine starting speeds, the induced voltage in coil 26 can be insufficient to drive transistor 20 and produce a sufficient voltage pulse to acutate the circuit and fire the engine. A sufficient voltage surge is obtained, however, from supplemental amplifying means such as capacitor 14. This capacitor is charged when switch 12 is closed. The induced voltage of pick-up coil 26 increases the voltage drop across capacitor 14 sufficiently to discharge the capacitor and the surge of current through load resistor 18 generates a sufficient voltage surge in the emitter-base circuit to bias transistor 20 into amplification, conducting current through connector 44 and resistor 24 to the negative ground.

The current pulse through resistor 24 causes the voltage at point A to become more positive, momentarily. This resistor is in the emitter-base circuit of transistor 48 and, accordingly, transistor 48 is momentarily turned into a conducting mode, permitting current flow through resistor 54, through the transistor and resistor 50 to the negative ground. Transistor 48 serves as an emitter-follower to provide sufficient current to bias transistor into saturation.

The current surge through resistor 50 generates a voltage drop across the resistor which causes the voltage at point B to become more positive, momentarily, until it biases transistor 70 into saturation, permitting current flow from positive lead 60 through the primary winding 62 to the ground through conductor 72.

As the rib 34 separates from its direct alignment with pole piece 38, the voltage induced in the pick-up coil 26 rapidly becomes more positive. When this voltage approaches the bias voltage of transistor 20, the voltage applied to the base of transistor 20 is sufficient to bias this transistor into a non-conducting mode. This causes the voltage at B to become sufficiently negative to bias transistor 70 into a non-conducting mode.

The opening of the circuit through the primary winding 62 causes a sudden collapse of the magnetic field in the coil and, in the conventional manner, induces a high voltage in the secondary winding 76. This high voltage is applied by high voltage lead 79 to the center post of the distributor and rotor 82 which directs it to the appropriate contact 84 and spark plug lead in a timed manner. The circuit now remains open until the next rib 34 approaches the pole piece 38.

The discharge of the high voltage inducedin the secondary winding 76 can induce a voltage surge of opposite potential in the primary winding 62 which, if applied to the collector 68, could damage transistor 70. The Zener diode 71 protects the transistor from this voltage surge by conducting the reverse current from the voltage surge to ground.

The characteristics of the Zener diode are chosen to insure that it conducts and cuts off the back-induced voltage at a value that will not damage the transistor 70, yet at a sufficiently high value so that the voltage of the secondary is not significantly reduced by conduction of this back-induced voltage.

Preferably, silicon transistors are used in the circuit and transistor 70 has a break-down voltage over 300 volts which is sufficient to permit it to be used with conventional coils having from 75 to about secondary turns per primary turn and conventional ballast resistors having from about 0.4 to about 2.0 ohms resistance.

FIG. 4 illustrates the voltage wave form for an eight cylinder engine as a function of degrees shaft rotation at a constant engine speed, typically at 1000 revolutions per minute. The start of the wave form cycle is shown at the point when the circuit is turned on by a sufficient induced voltage surge in coil 26. The battery voltage is applied across winding 62 and is removed at rotation. The circuit remains off until, at about 45 rotation, the induced voltage pulse in pick-up coil 26 is again sufficient to actuate the circuit and reapply the battery voltage. The charging and firing cycle is then repeated.

The system as thus described is in the off position for most of the ignition time and is turned on only for a sufficiently long time to achieve saturation or near saturation current flow in the primary winding 62. This contrasts with conventional point systems where current flows through the coil primary most of the time and is interrupted only momentarily to collapse the magnetic field of the primary winding and induce the high tension voltage to fire the spark plugs. The period that the circuit is closed is commonly referred to as dwell and the degree of rotation of the distributor shaft during this period as degrees of dwell. With a conventional point system, the points are closed for about 30 shaft rotation in an eight cylinder engine distributor. At low engine speeds, e.g., up to about 2,000 to 3,000 revolutions per minute, this far exceeds the amount of time which is required to saturate the primary of the coil, however, at higher engine speeds, the large angle of dwell is needed to permit sufficient time to reach saturation current in the primary. Accordingly, a comprise is made in the design of the conventional system because of the inflexibility of its dwell time with engine speed.

Because of the substantial variation in resistance of the ballast resistor and coil in the ignition systems of the different manufacturers, a system which is universally adaptable to all systems should limit the angle of dwell to a minimal value, thereby limiting the power loading on the transistors and power losses through the system with their concurrent heat development.

It has been found that the characteristics of the voltage pick-up coil and pulse amplification circuit of this invention are ideally suited for adaptation to widely varied ignition systems. The magnetic pick-up coil has been found to have characteristics which, in effect, increase the degrees of dwell with increase in engine speed. This apparently is caused by the fact that a finite time is required for the induced voltage in the pick-up coil to decrease after the rib 34 has separated from the pole piece 38 and this time remains relatively independent of the rotational speed of wheel 32. Consequently, the angle of dwell can be set to a much more narrow band than with a conventional point ignition system. Although not shown in FIG. 4, the effect would be to broaden the width w of the illustrated wave form at higher engine speeds. Since the advance mechanisms of the distributor are operative this would tend to shift the leading edges of the broadened wave form to the left in the illustration as the engine speed increases.

The following table summarizes typical values of the dwell degrees with conventional system and with the invention:

Distributor Shafi (Dwell) Degrees Invention at Variation between makes and models not speed responsive It has been found that engines equipped with the distributor modifications and circuit of this invention can be operated at engine speeds up to about 10,000 revolutions per minute without encountering any difficulties with ignition. In contrast, the dwell time for the conventional system usually becomes limiting and insufficient current flow is developed in the coil primary winding at engine speeds in excess of about 5000 revolutions per minute.

The aforestated values for dwell degrees have been found to be optimum for compatibility with the conventional coil and ignition equipment of present engines. The values can be varied, as desired, to tailor an installation to a particular system by changing the magnetic coupling characteristics between the flux wheel and magnet. To illustrate, changes in the coupling characteristics can be made to provide a more narrow band of dwell degrees, e.g., to about percent of the aforementioned values, for coils in which the primary current can be built up to saturation in a shorter time, or conversely, to provide a wider band of dwell degrees, e.g., to about percent of the aforementioned values, for use with coils requiring a longer time to reach saturation current.

The invention has been described with reference to a preferred embodiment adapted for use in negative ground installations and with a typical eight cylinder engine and distributor. It is of course apparent that the circuit can be readily adapted to positive ground'systerns and to other distributors and engines. Thus the invention can be used with special dual point distributors or with engines of less or more cylinders with obvious modifications. It is not intended that the illustrated and preferred embodiment be construed as unduly limiting of the invention. Instead, it is intended that the invention be defined by the means, and their obvious equivalents, set forth in the following claims.

What is claimed is:

1. An ignition system for an internal combustion engine having a storage battery, a distributor and coil with primary and secondary windings with connector means between the high tension post of the secondary and the rotor of the distributor which comprises:

a. primary circuit means to supply battery voltage to the primary of said coil;

b. a switching transistor with the emitter and collector thereof connected in circuit in said circuit means;

0. base biasing circuit means biasing said switching transistor into a non-conducting mode;

d. voltage pulse generating means comprising a magnetic field, means to vary the magnetic flux of said field in response to the rotational speed of an engine and to generate a cyclic variation of said magnetic flux for each cylinder of said engine in a timed manner and pick-up coil means positioned in said field for generation of a timed train of induced voltage pulses responsive to said cyclic variation of said magnetic flux;

e. amplifier means normally biased into a nonconducting mode; and connected for conduction in response to said voltage pulses, whereby said voltage pulses generate a timed train of amplified pulses from said amplifier; and

means to apply said train of amplified pulses to said base biasing means of said switching transistor to forward bias said switching transistor momentarily into a conducting mode only during the duration of each of said voltage pulses thereby applying battery current to the said primary windings of said coil for momentary periods sufficient to reach substantial saturation current in said primary.

2. The ignition system of claim 1 wherein a Zener diode is connected in said primary circuit means, parallel to said switching transistor and oriented to conduct reverse current surges induced in said primary by discharges from the secondary winding.

3. The ignition system of claim 1 wherein said amplifier means includes an amplifier transistor with conductor means to apply battery voltage between the emitter and collector and between the base and emitter thereof to bias said transistor into a non-conducting mode, amplifier-transistor base biasing circuit means therefor including said pick-up coil connected between said base and emitter whereby said induced voltage surges provide forward bias to drive said amplifier transistor into momentary conducting modes.

4. The ignition system of claim 3 including a third transistor in an emitter follower circuit to said amplifier transistor, conductor means to apply the train of ampli fied, momentary voltage surges from said amplifier transistor to the base of said third transistor and conductor means to apply the resultant train of further am plified voltage surges to the base biasing circuit of said switching transistor.

5. The ignition system of claim 1 wherein the duration of said momentary periods increase with increased speed of said engine.

6. The ignition system of claim 5 wherein the dura tions of said momentary periods at an engine speed of 1000 revolutions per minute are from to percent of 15 dwell degrees.

7. The ignition system of claim 6 wherein the duration of said momentary periods at an engine speed of 4000 revolutions per minute are from 75 to 125 percent of 30 dwell degrees.

8. The ignition system of claim 1 including capacitive means in circuit to said amplifier means and in parallel connection to said pick-up coil means.

9. The ignition system of claim 3 wherein said amplifier-transistor base biasing means includes resistance means in circuit between said base and emitter of said amplifier transistor.

10. The ignition system of claim 9 including capacitive means in said amplifier-transistor base biasing means in parallel connection to said pick-up coil means.

11. In an ignition system for a multi-cylinder internal combustion engine having a coil comprising primary and secondary windings, circuit means in series with said primary winding and including inductive coil means for magnetically producing a train of voltage pulses in time with the rotation of an engine the improvement comprising:

bias means connected to said circuit means to bias said circuit into a non-conduction and means to apply said train of voltage pulses to said bias means for momentarily rendering said circuit means conductive only during the duration of each of said voltage pulses.

12. The ignition system of claim 11 including capacitive means in said bias means in parallel connection to said inductive means.

13. The ignition system of claim 11 wherein said circuit means includes switching transistor means.

14. The ignition system of claim 13 wherein said means to apply said train of voltage pulses includes amplifier means in circuit to the biasing means of said switching transistor means. 

1. An ignition system for an internal combustion engine having a storage battery, a distributor and coil with primary and secondary windings with connector means between the high tension post of the secondary and the rotor of the distributor which comprises: a. primary circuit means to supply battery voltage to the primary of said coil; b. a switching transistor with the emitter and collector thereof connected in circuit in said circuit means; c. base biasing circuit means biasing said switching transistor into a non-conducting mode; d. voltage pulse generating means comprising a magnetic field, means to vary the magnetic flux of said field in response to the rotational speed of an engine and to generate a cyclic variation of said magnetic flux for each cylinder of said engine in a timed manner and pick-up coil means positioned in said field for generation of a timed train of induced voltage pulses responsive to said cyclic variation of said magnetic flux; e. amplifier means normally biased into a non-conducting mode; and connected for conduction in response to said voltage pulses, whereby said voltage pulses generate a timed train of amplified pulses from said amplifier; and f. means to apply said train of amplified pulses to said base biasing means of said switching transistor to forward bias said switching transistor momentarily into a conducting mode only during the duration of each of said voltage pulses thereby applying battery current to the said primary windings of said coil for momentary periods sufficient to reach substantial saturation current in said primary.
 2. The ignition system of claim 1 wherein a Zener diode is connected in said primary circuit means, parallel to said switching transistor and oriented to conduct reverse current surges induced in said primary by discharges from the secondary winding.
 3. The ignition system of claim 1 wherein said amplifier means includes an amplifier transistor with conductor means to apply battery voltage between the emitter and collector and between the base and emitter thereof to bias said transistor into a non-conducting mode, amplifier-transistor base biasing circuit means therefor including said pick-up coil connected between said base and emitter whereby said induced voltage surges provide forward bias to drive said amplifier transistor into momentary conducting modes.
 4. The ignition system of claim 3 including a third transistor in an emitter follower circuit to said amplifier transistor, conductor means to apply the train of amplified, momentary voltage surges from said amplifier transistor to the base of said third transistor and conductor means to apply the resultant train of further amplified voltage surges to the base biasing circuit of said switching transistor.
 5. The ignition system of claim 1 wherein the duration of said momentarY periods increase with increased speed of said engine.
 6. The ignition system of claim 5 wherein the durations of said momentary periods at an engine speed of 1000 revolutions per minute are from 75 to 125 percent of 15 dwell degrees.
 7. The ignition system of claim 6 wherein the duration of said momentary periods at an engine speed of 4000 revolutions per minute are from 75 to 125 percent of 30 dwell degrees.
 8. The ignition system of claim 1 including capacitive means in circuit to said amplifier means and in parallel connection to said pick-up coil means.
 9. The ignition system of claim 3 wherein said amplifier-transistor base biasing means includes resistance means in circuit between said base and emitter of said amplifier transistor.
 10. The ignition system of claim 9 including capacitive means in said amplifier-transistor base biasing means in parallel connection to said pick-up coil means.
 11. In an ignition system for a multi-cylinder internal combustion engine having a coil comprising primary and secondary windings, circuit means in series with said primary winding and including inductive coil means for magnetically producing a train of voltage pulses in time with the rotation of an engine the improvement comprising: bias means connected to said circuit means to bias said circuit into a non-conduction and means to apply said train of voltage pulses to said bias means for momentarily rendering said circuit means conductive only during the duration of each of said voltage pulses.
 12. The ignition system of claim 11 including capacitive means in said bias means in parallel connection to said inductive means.
 13. The ignition system of claim 11 wherein said circuit means includes switching transistor means.
 14. The ignition system of claim 13 wherein said means to apply said train of voltage pulses includes amplifier means in circuit to the biasing means of said switching transistor means. 